Cyclist coasting down a hill cons. of energy

[totallyclone]

Homework Statement

A bicyclist coasts down a 7.0° hill at a steady speed of 5.0m/s. Assuming a total mass of 75kg (bicycle plus rider), what must be the cyclist's power output to climb the same hill at the same speed?

Homework Equations

E_K=1/2 mv²
E_G=mgh
P=W/T

The Attempt at a Solution

I tried the question and this is what I got but I'm answer if this is right... not sure if there's a Force of friction though because I read the question and assumed there isn't any force of friction... but I'm unsure...

P=W/T
P=-W_GΔdcos180°/T
P=-W_Gvcos180°
P=-mgsin7.0°(5.0)cos180°
P=-(75)(9.8)sin7.0°(5.0)cos180°
P=448W

 

[kontejnjer]

Well if the cyclist goes down the hill with constant speed, then there must be some kind of force that's stopping him from accelerating, so you should account for it accordingly.

 

[tiny-tim]

hi totallyclone!

A bicyclist coasts down a 7.0° hill at a steady speed of 5.0m/s. Assuming a total mass of 75kg (bicycle plus rider), what must be the cyclist's power output to climb the same hill at the same speed?
…
not sure if there's a Force of friction …

he couldn't coast (at a steady speed) if there wasn't friction, could he?

 

[totallyclone]

hi totallyclone!


he couldn't coast (at a steady speed) if there wasn't friction, could he?

so...THERE'S FRICTION!?

 

[tiny-tim]

yup!